Potentiometer



y 6, 1965 F. J. MOORE, sR., ETAL 3,193,786

POTENTIOMETER Filed y 21, 5 2 Sheets-Sheet 1 56Z B 52 INVENTORS FRED J.MOORE, 67?. Y GEOFFREY SOUTHWEZL ATTORNEY y 6, 1955 F. J. MOORE, sR.,ETAL 3,193,786

POTENTIOMETER Filed y 21, 1963 2 Sheets-Sheet 2 INVENTORS /06 F950 .1.MOORE. 5R.

7 BY GEOFFREY SOUTHWELL //4 /09 52 Mw United States Patent 3,193,786POTENTIQMETER Fred J. Moore, Sr., Largo, and Geoffrey Southwell, St.Petershurg, Fla., assignors to International Resistance Company,Philadelphia, Pa.

Filed May 21, 1963, Ser. No. 282,032 6 Claims. (Cl. 338-464) The presentinvention relates to a potentiometer, and more particularly to aminiature trimmer potentiometer.

A trimmer potentiometer is a variable resist-or the resistance value ofwhich is not constantly changed, but which is set and maintained at :adesired resistance value until adjustment of the circuit is required.With the trend in the electronic industry toward miniaturization, it isdesirable to have very small and compact trimmer potentiometers. Also,because of the use of such trimmer potentiometers in electroniccircuits, it is desirable to be able to stack mount a plurality of thepotentiometers in side-byside' and/or end-to-end relation with all ofthe 3,193,785 Patented July 6, 1965 walls of the base. Base 12 isprovided with a cylindrical recess in its top surface, which recess hasa cylindrical wall 16 and a bottom surface 18. The cylindrical wall 16is interrupted by notches 20, 22, 24 and 26 extending through the baseatthe midpoint of each side of the base. A square cavity 28 is provided inthe bottom surface 18 wtih the corners of the cavity being at themidpoints of the sides of the base 12. A cylindrical hub 36 projectsupwardly from the center of the bottom of the cavity 28, and a rib 32extends radially from the hub 30 along the bottom of the cavity 23 tothe notch 26. A projection 34 extends upwardly from the bottom of thenotch 26 at the end of the rib 32. Rib 32 has a groove 36 in its uppersurface. The groove 36 extends longitudinally along the rib 32, andopens into a groove 38 in the hub 30. The groove 38 extends radiallyacross the hub 30 to the center of the hub. As shown in FIGURE 3, a hole40 extends adjustment knobs being exposed for ease of adjusting the Iresistance value setting of the potentiometers. In addition, theotentiometers are mounted sometimes with the adjustment knobs facingupwardly and sometimes with the adjusment knob facing forwardly.Therefore, it is desirable to have a potentiometer which can be easilymounted with the control knob facing in any desired direction.

It is an object of the present invention to provide a potentiometerwhich is compact and small in size.

It is another object of the present invention to provide a potentiometerwhich can be easily stack mounted in end-to-end and/ or side-by-siderelation with other similar potentiometers.

It is still another object of the present invention to provide aminiature potentiometer which is effectively sealed against moisture.

It is a further object of the present invention to provide a miniaturepotentiometer having either a top or a side adjustment.

It is a still further object of the present invention to provide aminiature potentiometer having a high degree of reliability andaccuracy, but being of economical construction.

Other objects will appear hereinafter.

For the purpose of illustrating the invention there is shown in thedrawings forms which are presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

. FIGURE 1 is a perspective view of the potentiometer of the presentinvention.

FIGURE 2 is an exploded perspective view of the potentiometer of thepresent invention.

FIGURE 3 is a sectional view taken along line 33 of FIGURE 1.

FIGURE 4 is a sectional view taken along line 4-4 of FIGURE 3.

FIGURE is a sectional view taken along line 5-1; of FIGURE 3.

FIGURE 6 is a sectional view similar to FIGURE 3 showing a modificationof the potentiometer of the present invention.

Referring to the drawings, the potentiometer of the present invention isgenerally designated as 10. As shown in FIGURE 1, potentiometer issubstantially cubical, and has no shaft protrusions. The potentiometer10 can be made as small as on each side.

Referring to FIGURES 2 and 3, potentiometer 10 comprises a substantiallyrectangular base 12 molded of an electrically insulating plastic. At thebottom of the base 12, a square supporting flange 14 projects from theside through the base 12 from the bottom of the groove 36 at the outerend of the groove. As shown in FIGURE 2, a pair of holes 42a and 425extends through the base 12 from the bottom of the cavity 28 atdiagonally opposite corners of the cavity.

An electrical resistance element, generally designated as 44, is mountedon the base 12. Resistance element 44 comprises a core 46 of anelectrical insulating material which is circular in transversecross-section. A resistance wire 43 is helically wound around and alongthe core 46. Resistance element 44 is in the form of an annulus with theends of the resistance element being spaced slightly I apart. As shownin FIGURE 3, the resistance element 4 4 is seated on the bottom surface18 of the recess in the base 12, and around the cylindrical Wall 16. Theends of the resistance element 44 are seated on the top surface of theprojection 34.

As shown in FIGURES 3 and 5, a pair of termination strips 50a and 5% areprovided under the ends of the resistance element 44. Termination strips50a and 5d!) are Of an electrically conductive metal, and are secured tothe end portions of the resistance wire winding 48, such as bysoldering, brazing or welding. The termination strips 50a and 50b extendinwardly of the resistance element 44 across the cavity 28 on oppositesides of the hub 30. A pair of terminal wires 52 and 54 extend throughthe holes 42a and 42b in the base 12. The top end portions 52a and 54aof the terminal wires are bent to extend along the cavity 28, andbeneath the termination strips 59a and 50b respectively (see FIGURE 5The termination strips Slla and 5% are secured to the top and portions52a and 54a of the terminal wires, such as by welding, brazing orsoldering. Thus, the terminal wires 52 and 54 are electrically connectedto the ends of the resistance element 44 through the termination strips50a and 5%.

A contact terminal wire 56 of an electrically conductive metal extendsthrough the hole 40 in the base 12.

The upper portion of the contact terminal wire 56 is bent A contactmember, generally designated as 58, is made from a flat sheet ofresilient, electrically conductive metal and is rotatably supported onthe top end portion 56b of the contact terminal wire 56. Contact member58 comprises a' circular plate 60 having a central hole 62 therethrough.A resilient contact arm 64 extends radially from the plate 60, and has aU-shaped contact finger 66 at the end thereof. A resilient slip ringcontact arm 68 extends I from the plate 68 diametrically opposite thecontact arm 64. Slip ring contact arm 68 is provided with a hole 78'therethrough, and a slip ring wiper contact 71 projecting downwardlyfrom the edge of the hole 70 adjacent the free end of the contact arm 68(see FIGURE 3). The contact plate 66 is seated on the top surface of hub38 with the contact arm 68 being bent over the plate 68 so that hole '70is over hole 62 in the plate 60. The top end portion 56b of the contactterminal wire 56 extends through the holes 62 and 78 in the plate 60 andresilient slip ring contact arm 68 thus applying pressure to terminalcontact wire 56b through slip ring wiper contact 71. Thus, the contactmember 58 is rotatably supported on and electrically connected to thecontact terminal wire 56. Contact arm 64 is of a length so that thecontact finger 66 extends over the resistance element 44. When theresilient contact member 58 is held in position on hub 38, the contactarm 64 is bent so that pressure is applied to contact finger 66 to holdthe contact finger in slidable engagement with the resistance element44.

A cylindrical actuator knob, generally designated as 72, of anelectrical insulating material is rotatably mounted on the base 12. Acylindrical flange '74 projects radially outwardly from the knob 72adjacent to but spaced from the top end thereof. The knob 72 is providedwith a cylindrical recess 76 in its bottom surface, a slot 78 extendingdiametrically across the bottom portion thereof beneath the flange 74,and a blind hole 86 in the center of the bottom of the slot 78. Therecess 76 is of a diameter equal to the diameter of the hub 38 of thebase 12. The slot 78 is of a width to receive the contact member 58. Thehole 88 is of a diameter equal to the diameter of the contact terminalwire 56. An annular groove 82 is provided in the top surface of theflange 74 concentric with the top portion of the knob 72. A stop lug 84projects radially outwardly from the periphery of the flange 74 (seeFIGURES 2 and 4). Actuator knob 72 is provided with a slot 86 extendingdiametrically across the center portion of the top end thereof. Aprojection 88 in the form of an arrow head extends upwardly from the topend of the knob 72 at one end of the slot 86. (See FIGURES l and 2.) Theactuator knob 72 is mounted on the base 12 with the hub 30 fittingwithin the recess 76 in the knob, the top end portion 56a of the contactterminal wire 56 fitting in the hole 80 in the knob, and the contactmember 58 being within the slot 78 in the knob. Thus, the knob 72 issupported on the base 12 for rotation about the hub 30 and the top endportion 56b of the contact terminal wire 56. When the knob 72 isrotated, the side walls of the slot 78 engage the sides of the contactarm 64 to rotate the contact member 58.

A cover, generally designated as 90, of an electrical insulatingmaterial is mounted on the base 12, and encloses the knob 72, contactmember 58 and resistance element 44. Cover 90 has a square flat top 92,and rectangular flat sides 94. The free ends of the sides 94 are seatedon the flange 14 of the base 12, and are secured thereto, such as by asuitable cement. The top 92 of the cover 90 is provided with a central,circular hole 96 therethrough through which the top end portion of theknob 72 extends. On the inner surface of the top 92 of the cover 98there is provided an annular projection 98 which is concentric with thehole 96. The projection 98 is semi-circular in transverse cross-sectionand is directly over the annular groove 82 in the flange I4 of the knob72. A normally flat, annular sealing washer 100 is provided between theprojection 98 and the groove 82 in the flange 74 of the knob. As shownin FIGURE 3, the projection 98 bends the sealing washer 100 into thegroove 82 so as to provide a seal between the flange 74 and the top 92of the cover. As shown in FIGURE 4, a stop lug 102 projects inwardlyfrom the sides 94 of the cover across the path of travel of the stop lug84 on the flange 74 of the knob 72. As shown in FIGURES 1 and 2, the top92 of the cover 90 is provided on its outer surface with a plurality ofraised indicating marks 164 uniformly spaced around the hole 96 in thetop. The odd numbered indicating marks 184 are provided with an indicianumber. One side 94 of the cover 98 is provided with a shallow groove106 in its outer surface extending from the free edge thereof. Groove106 is in alignment with a notch 188 in the edge of the flange 14 of thebase 12. One purpose of the groove 106 and notch 108 is to permit easeof properly mounting the cover 96 on the base 12.

In the operation of the potentiometer 16 of the present invention, theresistance value thereof is varied by inserting a screw driver orsimilar instrument in the slot 86 in the top end of the actuator knob72, and rotating the knob. Rotating the actuator knob 72 rotates thecontact memher 58 so as to slide the contact finger 66 along theresistance element 44. Since the contact member 58 is electricallyconnected to the contact terminal wire 56, movement of the contactfinger 66 along the resistance element 44 varies the electricalresistance between the contact terminal wire 56 and the terminal wires52 and 54, which are electrically connected to the ends of theresistance element. The stop lugs 84 and 162 are arranged so that whenthe contact finger 66 is at the ends of the resistance element 44, thestop lug 84 engages the stop lug 102 to prevent further rotation of theactuator knob 72. Thus, the contact finger 66 is prevented from beingmoved across the space between the ends of theresistance element 44, andis limited to being moved only along the length of the resistanceelement. The arrow head projection 88 on the top surface of the actuatorknob 72 is positioned directly over the contact arm 64, and the zero and10 indicating marks 104 are located directly over the ends of theresistance element 44. Thus, the arrow head projection 88 and indicatingmarks 104 provide an indication of the position of the contact finger 66along the resistance element 44. Since the potentiometer It) is in theshape of a cube, and all of the terminal wires project from the base ofthe potentiometer, a plurality of the potentiometers 10 can be mountedin side-by-side relation on a mounting panel or printed circuit board.Thus, a plurality of the potentiometers of the present invention can bemounted together in a minimum amount of space, yet with the actuatingknobs of the potentiometers exposed to permit ease of adjustment of thepotentiometers.

The potentiometer 16 of the present invention is constructed so thatwhen it is mounted on a printed circuit board or similar mounting panel,it is adjustable from the top. However, it is often desirable to mountthe potentiometer so that it is adjustable from the side. FIGURE 6.shows the potentiometer 10 of the present invention modified so that itis adjustable from the side when mounted on a printed circuit panel orthe like. To so modify the potentiometer 10, a L-shaped plate, generallydesignated as 118, is mounted on the potentiometer 10, such as by asuitable cement. Plate 110 has a rectangular base leg 112 which extendsacross the base 12 of the potentiometer, and a rectangular side leg 114which extends across the sides 94 of the potentiometer which has thegroove 186 therein. The base plate 112 is provided on its inner surfacewith a groove 116 which extends from the hole 40 in the base 12 to agroove 118 in the inner surface of the side leg 114 which is inalignment with the groove 106 in the side of the potentiometer.

A hole 126 extends through the side leg 114 at the end of the groove118. The contact terminal wire 56 is bent to extend along the grooves116 and 118, and through the hole 120 to project from the side of thepotentiometer 10. The base leg 112 of the plate 110 is also provided onits inner surface with a pair of grooves and holes, not shown, throughwhich the terminal wires 52 and 54 extend so that the terminal wires 52and 54 also project from the side of the potentiometer 19. Thus, whenthe potentiometer 10 modified with the plate 110 is mounted on a printedcircuit board or the like, the actuator knob 72 is side adjustable.

Thus, there is provided by the present invention a trimmer potentiometerwhich is compact and small in size, and which can be easily stackmounted in side-by-slde relation with other similar potentiometers.Also, the potentiometer of the present invention can be easily modifiedfor either side or top adjustment when mounted on a printed circuitboard or the like. Although the potentiometer of the present inventionhas a high degree of reliability and accuracy, it is of economicalconstruction since it is made up of a minimum number of parts. Inaddition, the potentiometer of the presentinvention is effectivelysealed against moisture.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof, andaccordingly, reference should be made to the appended claims, ratherthan to the foreging specification as indicating the scope of theinvention.

' We claim:

1. A potentiometer comprising a base, an annular re sistance elementmounted on a surface of said base with the ends of the resistanceelement being spaced apart, a pair of terminal wires extending throughsaid base, each of said terminal wires being electrically connected to aseparate end of said resistance element, a contact terminal wireextending through said base and projecting beyond said surface of thebase at the center of the resistance element, a contact member of anelectrically conducting metal rotatably mounted directly on andcontacting the projecting portion of the contact terminal wire and so asto be electrically connected thereto, said contact member having acontact arm slidably engaging the resistance element, an actuator knobmounted and supported on said surface of the base and rotatable aboutthe projecting portion of the contact terminal wire, said actuator knobdrivingly engaging said contact member so that rotation of said knobrotates the contact member, and a cover mounted on said base andencompassing the resistance element, contact member and actuator knob,said cover having an opening therethrough through which the actuatorknob extends.

2. A potentiometer in accordance with claim 1 in which the contactmember comprises a contact plate having a hole therethrough, the contactarm extends from an edge of the contact plate, and a second arm extendsfrom an edge of the contact plate and is bent back over the contactplate, said second arm having a hole therethrough over the hole in thecontact plate, and the projecting portion of the contact terminal wireextends through the 6 holes in the contact plate and second arm so thatthe contact member is rotatable around the contact terminal wire. 7

3. A potentiometer in accordance with claim 2 in which the base has acylindrical hub projecting from its said surface at the center of theresistance element, the projecting portion of the contact terminal wireextends from the center of the hub, and the actuator knob has acylindrical recess in its bottom surface which receives the hub and ablind hole therein which receives the projecting portion of the contactterminal wire so that the knob is rotatably supported on the hub and thecontact terminal wire.

4. A potentiometer in accordance with claim 3 in which the actuator knobhas a slot extending transversely thereacross at the bottom end thereof,the contact member fits in said slot with the contact arm projectingbeyond the knob, the side walls of said slot engaging the contact memberso that rotation of said knob rotates the contact member.

5. A potentiometer in accordance with claim 1 in which the actuator knobhas an annular flange juxtaposed to the inner surface of the top of thecover, and sealing means is provided between said flange and the cover.

6. A potentiometer in accordance with claim 5 in which the actuator knobflange has an annular groove in its surface which faces the top of thecover, the top of the cover has an annular projection directly over thegroove in the flange, and a sealing ring is compressed between saidprojection and the groove.

References (lited by the Examiner UNITED STATES PATENTS 1,465,872 8/23Schoenung 1 338 2,406,503 8/46 Miller 338-164 2,765,384 10/56 Arisman338-197 2,839,642 6/58 Dickinson et a1 338174 X 2,884,506 4/59 Graustein338 -175 X 3,096,499 7/63 Hudson et a1 338--174 X 3,105,949 10/63Zarillo 338174 FOREIGN PATENTS 250,766 4/26 Great Britain. 684,067 12/52Great Britain.

63,137 3/55 France.

RICHARD M. WOOD, Primary Examiner.

ANTHONY BARTIS, Examiner.

1. A POTENTIOMETER COMPRISING A BASE, AN ANNULAR RESISTANCE ELEMENT MOUNTED ON A SURFACE OF SAID BASE WITH THE ENDS OF THE RESISTANCE ELEMENT BEING SPACED APART, A PAIR OF TERMINAL WIRES EXTENDING THROUGH SAID BASE, EACH OF SAID TERMINAL WIRES BEING ELECTRICALLY CONNECTED TO A SEPARATE END OF SAID RESISTANCE ELEMENT, A CONTACT TERMINAL WIRE EXTENDING THROUGH SAID BASE AND PROJECTING BEYOND SAID SURFACE OF THE BASE AT THE CENTER OF THE RESISTANCE ELEMENT, A CONTACT MEMBER OF AN ELECTRICALLY CONDUCTING METAL ROTATABLY MOUNTED DIRECTLY ON AND CONTACTING THE PROJECTING PORTION OF THE CONTACT TERMINAL WIRE AND SO AS TO BE ELECTRICALLY CONNECTED THERETO, SAID CONTACT MEMBER HAVING A CONTACT ARM SLIDABLY ENGAGING THE RESISTANCE ELEMENT, AN ACTUATOR KNOB MOUNTED AND SUPPORTED ON SAID SURFACE OF THE BASE AND ROTATABLE ABOUT THE PROJECTING PORTION OF THE CONTACT TERMINAL WIRE, SAID ACTUATOR KNOB DRIVINGLY ENGAGING SAID CONTACT MEMBER SO THAT ROTATION OF SAID KNOB ROTATES THE CONTACT MEMBER, AND A COVER MOUNTED ON SAID BASE AND ENCOMPASSING THE RESISTANCE ELEMENT, CONTACT MEMBER AND ACTUATOR KNOB, SAID COVER HAVING AN OPENING THERETHROUGH THROUGH WHICH THE ACTUATOR KNOB EXTENDS. 